The present invention deals with power machines. More particularly, the present invention deals with an arrangement of valves in a power machine to provide multiple functions.
Mini-excavators are currently in wide use. Such excavators typically have a base portion which is supported by a pair of track assemblies. The track assemblies are powered by hydraulic motors.
The base portion typically supports a house, or operator support portion. The house is rotatable relative to the base portion. Rotation is powered by a hydraulic slew motor. Mini-excavators also typically have a number of other features. For example, a boom is typically coupled to the house. A power actuator, such as a hydraulic cylinder, is coupled to the boom to pivot the boom relative to the house about an arc substantially located in a vertical plane. The boom is also typically pivotable substantially in a horizontal plane. This type of pivoting movement is accomplished through the use of a hydraulic cylinder (referred to as an offset cylinder) coupled to the house and to the boom.
An arm is coupled to a distal end of the boom, and is also typically pivotable relative to the boom through use of a hydraulic cylinder. A tool is commonly coupled to the end of the arm and is manipulated, also through the use of a hydraulic cylinder. Such a tool may typically be a bucket pivotally coupled to the arm.
Also, a blade is commonly mounted to the base portion. The blade can be raised, and lowered, by actuating a hydraulic cylinder. Other functions, such as auxiliary functions are also common.
While many hydraulic functions may be provided on the mini-excavator, there are typically four primary functions performed by the mini-excavator. The first is actuation of the bucket (or tool), the second is actuation of the arm, the third is actuation of the boom, and the fourth is operating the slew motor.
In prior excavators, the valves controlling these four hydraulic functions were placed in parallel with one another. Because of this parallel arrangement, if any of the functions were actuated simultaneously, the function requiring the least pressure obtained substantially all of the hydraulic fluid flow. Therefore, if two functions were actuated simultaneously, such as lifting the boom out of a hole, after the bucket is full of dirt, and rotating the cab (or house) the higher pressure of those functions would substantially stop while the other function was being performed.
Also, in prior excavators, it has been observed that two of the functions performed by the mini-excavator can tend to be more time consuming than the other functions. One of the time consuming functions is raising the boom, particularly when the bucket is filled with dirt or another heavy substance. The boom cylinder is generally quite a large cylinder and takes a great deal of hydraulic fluid for actuation. Providing enough hydraulic flow to the hydraulic actuator raising the boom can take significant time.
The other function which can be time consuming is traveling in the excavator. It has been conventional wisdom that hydraulic power supplied to the traction motors to move the excavator should be substantially separated from power provided to perform other functions in the hydraulic circuit. In other words, it has been thought advantageous to provide the traction motor hydraulic fluid in its own hydraulic circuit substantially separate from the circuit which provides hydraulic fluid to the remainder of the functions.
Also, prior excavators have been configured to provide multiple travel speeds. However, prior systems have provided this multiple speed function by providing a dual-displacement traction motor, which is quite expensive. Such a motor provides a different output speed, but at a lower torque.